This application claims the priority of German Application No. 196 42 831.9, filed Oct. 17, 1996, German Application No. 296 22 887.7, filed May 23, 1997, and German Application No. 197 24 040.2, filed Jun. 7, 1997, the disclosures of which are expressly incorporated by reference herein.
The invention relates to a process and apparatus for the application of self-adhesive protective film to vehicle bodies.
In the mass-production operation of a large number of passenger vehicle manufacturers, the vehicles must be prepared for dispatch in such a way that they do not suffer damage, in particular that the paintwork is not adversely affected by storage and weather influences. Where rail journeys or even ship transports are necessary for conveyance to the customer, the vehicles have been coated for this purpose with a protective layer of wax, which has had to be removed prior to customer delivery. The residue-free removal of the protective wax was not only a labour-intensive task, but also placed a strain upon man and the environment due to the solvent used therein. For this reason, there has recently been a move to protect vehicle bodies during transport by using self-adhesive films, though it has only been the essentially horizontal surface sections of the body, which are susceptible to damage by weather and by deposits, which have been protected in this way. Because this type of protection is not only very effective but also relatively dear, it has been provided not only as protection during transport but also as protection during vehicle assembly and consequently the protective film has been applied even before the final vehicle assembly, i.e. directly after the painting of the body.
The protective film is intended to be applied, as far as possible, in a crease-free and bubble-free manner, since, after a certain storage period, a microclimate can form under creases or bubbles, which, depending on paint type and colour, can sometimes result in visible marks. In order to be able to apply the protective films carefully, the film cuts had previously to be held by several persons, brought over the vehicle, aligned and placed against the associated surface sections. Despite the high expenditure of labour, creases and bubbles could not always be avoided in the application of the protective film.
When the regions for add-on parts were subsequently cut free, this often resulted in damage to the paintwork, thereby necessitating costly refinishing works. In the previous manual application of the protective film, the procedure was as follows: firstly, a rectangular piece of a protective film, which had been matched in size to a surface section, was drawn off and cut off from a feed roll by at least one or two persons, and the trailing end was held and cut off by one or two additional persons. This protective film piece was freely tensioned by as many as four persons in freehand manipulation with the self-adhesive side pointing downwards, brought in this way over the body, lowered there in positionally correct fashion in horizontal position onto the associated surface section, placed against it more or less free from creases and bubbles and pressed down by smoothing with a soft, slidable item, e.g. a stiffened piece of felt.
In the region of covered-over gaps between adjoining body parts such as wings or doors, the protective film was cut through manually with a knife and the cut edges pressed down by hand in order to shape the way in which assembly-relevant work was carried out. In order to be able to cut free and recess assembly-conforming holes in the protective film in the region of add-on parts such as roof trim rails, sliding roof cover, radiator figurine, windscreen washer nozzles, antennae, windscreen surrounds or the like, a flat, strip-shaped template was previously placed in positionally correct fashion onto the body and the protective film to be applied likewise stuck onto this, so that at the regions to be cut free not only was the film held at a slight distance from the body surface but also, as a result of the template, a cutting and guide edge for a knife is formed, along which the film can be cut through in conformity with the contour. Despite constant practice, the handling of a sharp-edged knife just a short distance from the painted body surface has repeatedly resulted, amidst the hustle and bustle, in paint damage and costly refinishing work. Particularly in body forms having, for example, beads in the region of the hood, the portion of film spanning the bead could previously be manually cut through only after a strip of film had been placed underneath, since there was too great a risk of paint damage in the region of the bead.
One object of the invention is to improve the application process and the corresponding appliance such that the monotonous manual work can be replaced by mechanization, the quality of the application in terms of freedom from bubbles and creases in the applied protective film, together with the avoidance of paint damage, can be improved and, moreover, savings can be made in labour costs.
Another object of the present invention is to provide a process for cutting through protective film in the region of stuck-over joints and beads, especially of passenger vehicle bodies, which helps to prevent paint damage and, moreover, offers possible savings in labor costs.
These and other objects and advantages are achieved by the method and apparatus according to the invention, in which a measured rectangular piece of a protective film is drawn off from a feed roll on the non-adhesive side using a robot-guided tensioning frame, preferably with suction arms, is drawn off and cut off from the feed roll. Before the film cut is placed against the body, while the film is stretched on the tensioning frame (which can be handled like a rigid workpiece) tear lines are perforated in the region of add-on parts, from the non-adhesive side of the film, using a heated serrated disc which is mechanically guided along defined contour lines. (Such performated tear lines allow specific areas of the film to be removed during the assembly process by tearing them off along the performations.)
Subsequently, the protective film, which has been thus prepared and tensioned in a crease-free manner in the tensioning frame, is lowered by the handling robots onto the associated surface section, placed in the correct position, free from bubbles, and pressed down with a smoothing bar. All surface sections are thereby successively covered over. In the region of add-on parts, protective film parts are drawn off along the perforated tear lines, and assembly-conforming holes are thus formed in these regions. Also, in the region of joints and beads which have been covered over, the film, according to the invention, is cut through by means of a robot-guided knife, the cut edges being pressed down, for example, using a rotary brush or an air nozzle.
The apparatus according to the invention is distinguished by a freely programmable industrial robot (cutting robot) having at least five degrees of motional freedom, and having an operating arm to which a cutting and pressing tool is fitted. As the cutting tool, a knife having a blade for cutting through the protective film in the region of covered-over joints and beads is provided. For pressing down the cut edges of the protective film, a suitable pressing tool is provided, which is disposed downstream of the cutting tool in the cutting and motion direction. According to the invention, the pressing tool is either a rotary brush, which can be placed onto the body is parts lined with the protective film, or an air nozzle, which is directed at the cut edges and the (preferably diffuse) air jet of which presses down the edges.
The use of the cutting robot ensures precise guidance of the knife for cutting through the protective film, so that the risk of paint damage is substantially reduced. In the region of a stuck-over joint or bead, the cutting robot thrusts the knife blade disposed on its operating arm through the protective film and moves the knife in the cutting direction predetermined by the joint or bead, up to the point where the end of the joint or bead is reached. As a result of the rotary brush, which is disposed behind the knife and which is placed directly (or through the lowering of the operating arm) on the body part lined with protective film, the cut edges of the cut-through protective film are pressed down onto the body, thereby precluding any detachment of the film due to protective film edges which fail to adhere to the body. In another embodiment of the invention, the cut edges are pressed down onto the body by means of an air nozzle disposed behind the knife, which emits a diffuse air current directed at the protective film.
In one design of the invention, the flat sides of the knife blade respectively have a plastic coating. Such a coating serves to prevent damage to the painted body through contact of the hard blade material with the paintwork if the knife-guidance direction should deviate slightly from the alignment of the joint. The plastic applied to both sides of the blade should have good sliding characteristics in relation to hardened vehicle paints and in relation to the protective film to be applied.
In a further design of the invention, the knife is elastically suspended in the cutting and pressing tool, transversely to the cutting and motion direction, by means of a leaf spring. As a result of this design according to the invention, inaccuracies between the robot-guidance of the knife and the actual course of the body joint or bead are compensated, since the knife, in the event of a lateral contact with the body part limiting the joint, can elastically "veer away". Advantageously, adjustable stop arms are provided to act upon the knife and/or the leaf spring, transversely to the cutting and motion direction, so that when the protective film is pierced, the stop arms serve to fix the knife. Following the insertion of the knife and during the cutting operation, the action of the stop arms upon the knife and the leaf spring is lifted, so that the desired elasticity takes effect whenever the knife comes into lateral contact with body parts.
In a particularly advantageous design of the invention, the knife is rearwardly pivotable, so that if during the cutting operation, it encounters an unforeseen obstacle in the cutting direction, it is pivoted rearwards in the cutting direction. This pivoting is detected by a suitable sensor and provokes an immediate withdrawal of the knife or of the operating arm of the cutting robot, so that an unforeseen and undesirable obstacle by which the knife is confronted in its cutting path does not bring the production line to a halt. Rather, the cutting robot travels to the next body joint or bead and systematically cuts it open. Protective films which have not been properly cut through are then treated in a downstream manual checking station. Alternatively, the cutting robot, after the knife is withdrawn, can skip the site of the obstacle and, beyond the obstacle, re-insert the knife into the protective film above the joint to be cut free, so as to continue with the cutting.
In a particularly advantageous design, the knife is disposed on a biaxial floating slide such that it is adjustable perpendicularly to the film plane and transversely to the cutting and motion direction. The floating slide is disposed, for its part, on the operating arm of the robot and allows, during a "search travel" prior to the commencement of the cutting operation, a fine adjustment of the knife in the z-direction (perpendicularly to the film plane). Following completion of this search travel, the z-floating slide is fixed and the knife is extended, either by movement of the operating arm of the cutting robot perpendicularly to the film plane or by direct extension of the knife. Immediately thereafter, the cutting operation is performed, with inaccuracies between the robot-guided cutting path of the knife and the body joint being compensated by the z-floating slide.
In an advantageous design, the cutting and pressing tool can be moved into a variety of operating settings and a measuring device is assigned to it, for registering within the working space of the cutting robot the actual position of those joints or beads of the body which are to be cut free.
The measuring device may be, for example, a measuring tool disposed on the cutting and pressing tool. In this case, the cutting and pressing tool can be swivelled into a variety of operating settings: in a first swivel setting the measuring tool is operative, and in a second swivel setting the cutting and pressing tool is operative. The measuring tool can advantageously comprise optical and/or acoustic sensors, by means of which the exact position of the gap to be cut free can be detected. As soon as the actual position of the gap has been determined, the cutting and pressing tool is pivoted so that the knife is aligned to the detected actual position of the gap and the cutting operation can commence.
In another design of the invention, a tactile probe which is adjustable on a biaxial floating slide perpendicularly to the film plane and transversely to the cutting and motion direction is provided as the measuring device. This probe can be lowered by the robot arm and/or directly onto the body, whereby the z-floating slide is deflected (perpendicularly to the film plane). The robot next performs with the tactile probe a motion running essentially transversely to the alignment of the joint. As soon as the probe is located in the joint gap, as the robot continues its travel, the y-floating slide is deflected (transversely to the cutting and motion direction), whereupon the probe remains in the gap. Following completion of the search travel, the z-floating slide is fixed. Armed with this knowledge of the actual position of the joint to be cut free, the knife can now be brought into the starting position for the cutting operation.
In a particularly advantageous design of the invention, the knife is disposed on the biaxial floating slide holding the probe, and the probe and the knife are adjustable perpendicularly to the film plane. Following completion of the search travel, the knife can thus easily be extended, whereby it pierces the protective film covering the gap, and the probe is retracted. In this manner, the cutting operation commences through the robot-guidance of the knife.
In another design of the invention, a tactile probe which is pivotable transversely to the cutting and motion direction is provided as the cutting device. In this design of the invention, the probe follows a search travel path which is essentially transverse to the gap to be cut, and is deflected as soon as it enters into the joint gap. The deflection is detected by means of a suitable sensor, and a signal is transmitted to the cutting robot, which stores the deflection point as a point of insertion for the knife. After having been stored, a deflection which has once been detected or an ascertained deflection path can also be used for an adjacent body joint or bead.
In one design of the invention, the tactile probe has a rounded feeler tip, and in another design it has a probe tip with a feeler roll matched to the gap.
In a further embodiment of the invention, a device for cutting through protective film in the region of covered-over joints and beads has an operating arm of the cutting robot with a cutting and pressing tool in the form of an air nozzle, which is suitable for a diffuse emission of hot air. The temperature of the hot air is set, for example, at least to the melting temperature of the plastic of the protective film. The appliance according to the invention allows the protective film to be cut through in a contact-free manner in the region of covered-over joints and beads. As a result of the hot air, the plastic of the protective film begins to melt, and is cut through in the region of a joint or bead by the pulse of the air current striking it. The particular advantage of this contact-free cutting resides in the fact that no additional pressing tool is necessary to press down the cut edges of the protective film, since the cut edges are already pressed down onto the body by the air current issuing from the air nozzle. Since the hot air is emitted from the air nozzle (that is, the air jet is directed not at a point, but only over an area, it is not absolutely necessary to provide a measuring device for fine alignment of the air nozzle. That is, any small deviations of the gap from the actual position are compensated by the diffuse air current.
In one design of the invention, a pin made from a material offering good heat conductivity is disposed in the region in front of the air-discharge opening of the air nozzle. This pin can advantageously be extended and serves to cut through the protective film, especially in the region of wide beads, whenever the pulse applied by the air current to the protective film, because of the width of the gap lying beneath the film, is insufficient to cut through this film.